In recent years, substances having a function of transmitting visible light rays satisfactorily while selectively blocking ultraviolet rays have been used in various fields. For example, in window glasses of automobiles, window glasses of buildings and the like, ultraviolet blocking glasses are widely used for blocking ultraviolet rays which cause sunburns and degradation of interior materials.
Molded products of transparent thermoplastic resins such as an acryl resin, a polycarbonate resin, a polyester resin and the like, to which a function of blocking ultraviolet rays is imparted, are also used in applications such as transparent resin plates used in car ports, show windows, show cases, transparent shades for illumination and the like and various kinds of transparent containers.
Thus, a method of using inorganic metal oxide fine particles or an organic ultraviolet absorbent as an ultraviolet absorbent is generally known for imparting to substrates such as glass, resins and the like a function of blocking ultraviolet rays.
However, for ultraviolet absorbents which have been known, irrespective of inorganic metal oxide fine particles or organic ultraviolet absorbents, ultraviolet rays which can be blocked are limited to those having a wavelength of 380 nm or less, and there are very little known ultraviolet absorbents which can satisfactorily block ultraviolet rays called UV-A of 380 to 400 nm, are not degraded even if irradiated with light for a long period, and transmit visible light satisfactorily.
Herein, UV-A refers to ultraviolet rays having a relatively long wavelength (320 to 400 nm), and is the most abundant of ultraviolet rays of sunlight which reach the ground, but is known to cause pigmentation (freckles) and wrinkles through long time exposure because it penetrates deep into the skin for the human body.